The present invention relates to a method and system for communication, and particularly, but not exclusively, to a method and system for providing secure communication without use of encryption.
In the communication field, it has long been accepted that there are two principal ways in which a message can be securely communicated between two parties: encryption and steganography.
Encryption generally involves replacing the “plain text” of the original message with a code which can (hopefully) only be decoded by the intended recipient. Current encryption technologies such as DES and RSA generally use either exchanged keys or a public/private key system.
Steganography involves “hiding” the plain text of the original message in another item that is communicated between the parties. This approach includes methods such as placing the plain text at agreed locations within a “cover” message, or communicating the plain text as part of the pixels of a picture. In all cases, the plain text of the original message is still present in its original, unencoded form, but only the intended recipient knows how to retrieve it from the “cover”.
Recently, a third method of secure communication has been suggested, principally in Chaffing and Winnowing: Confidentiality without Encryption by Ronald L. Rivest, CryptoBytes (RSA Laboratories), volume 4, number 1 (summer 1998), 12-17. This technique is called “chaffing”, as the principle is to provide sufficient “chaff” that only the intended recipient can sort out the “wheat” of the original message. Chaffing is similar in many respects to steganography, in that the original message is communicated between the parties without encryption, but only the intended recipient is able to retrieve the original message.
There is increasingly a demand for secure communication in all fields. This demand creates problems in fields where the devices used to transmit messages are relatively simple and need to be low cost, such as radio-frequency identifiers (RFIDs). Such devices are generally incapable of performing the complex routines required to encrypt their messages or of constructing and transmitting the cover message required for steganography.
The chaffing method described in Rivest above still requires the two communicating parties to have exchanged information in advance in order for the receiver to be able to distinguish the authentic Message Authentication Codes (MACs).
Accordingly, at its broadest, the present invention provides a communications system in which noise is transmitted over a range of communication channels, and the receiver is able to distinguish an original message by using information about that noise. A receiver which does not have information about that noise is not able to distinguish the original message.
A first aspect of the present invention provides a communications system including a receiver and a first transmitter, wherein:
the first transmitter transmits noise signals across a range of communication channels used by the receiver;
the receiver is adapted to receive a transmission transmitted by a second transmitter over one or more of said range of communication channels, and to distinguish the transmission made by the second transmitter from the noise signals using information from the first transmitter about the noise signals.
By using the above system, the second transmitter does not need to have any capability to encrypt or disguise its transmissions in order to securely transmit them to the receiver, as the security for those transmissions is provided by the noise transmissions from the first transmitter. Accordingly, the second transmitter can be made relatively simple and cheap to construct.
The information about the noise signals is preferably communicated from the first transmitter to the receiver. The information may be the complete content of the noise signals, which may contain a time stamp so that the signals can be compared to the received signals.
Alternatively or additionally, the information may be which channels the noise was transmitted over at particular times.
In a particular embodiment of the first aspect, the receiver and first transmitter are part of the same device. In this embodiment, the communication of the information about the noise signals may be achieved by the first transmitter having an internal output by which the noise is passed to the receiver, or by the receiver and the transmitter sharing a common memory or processor. In one specific embodiment, the first transmitter may receive driver signals from a processor, and the same driver signals may be provided to the receiver by the same processor.
The term “noise signals” is used to describe any signals which are not part of the transmissions from the second transmitter. Such signals need not be “noise” in the meaning of an entirely random signal, and preferably the noise signals are such that they are readily separable by the receiver from the transmissions from the second transmitter, e.g. by virtue of the channels over which they are transmitted.
Indeed, the content of the noise signals is preferably substantially identical to the transmissions made by the second transmitter. If this is the case, may be even more difficult for a third party or interloper to distinguish the transmissions from the second transmitter simply by analysing the content of the transmissions.
The range of communication channels may include one or more of: different time slots; different frequency bands; different orthogonal codes. The communications channels may also be Ethernet-type channels in which there are no defined slot and the transmitters wait for the medium to be idle before transmitting asynchronously.
A further aspect of the present invention provides a communications system according to the above first aspect, further including said second transmitter, the second transmitter transmitting over one or more of said communication channels.
In this aspect there may be a plurality of said second transmitters.
The or each second transmitter may be a simple device. Simple devices, sometimes known as “dumb” devices or tags, are limited in one or more of their computational power, their battery power or life, or their memory capabilities, and so are not capable of performing techniques such as encryption, which are expensive to perform in terms of those factors. For example the simple device may be one which simply transmits its own ID over a pre-selected communication channel, or one which can read only one frequency and one protocol. Thus it is unable to filter reads, store tag data and so on.
Although the present invention also covers second transmitters which are more complex, and indeed transmitters that may have considerable processing power, in this aspect of the present invention, that processing power is not required to disguise or encrypt the transmissions for security due to the noise transmission of the first transmitter.
In one typical example, the or each second transmitter is an RFID tag, and the receiver is an RFID reader or overseer tag.
Preferably, the receiver, the second transmitter or both are adapted to detect when a collision occurs on a particular channel, and cause the data lost in that collision to be retransmitted. If the system has this ability, then the first transmitter can transmit over all the possible communications channels without having to know what channels are being used by the second transmitter(s), as any collisions will be detected and the data lost retransmitted.
In the present description, references to “collision” are to situations where more than one demand is made simultaneously on the medium that is being used to communicate between the devices. The definition of this term at www.wikipedia.org reads: “In a data transmission system, the situation that occurs when two or more demands are made simultaneously on equipment that can handle only one at any given instant.”
“Collision” is a standard term of art in the description of Media Access Control (MAC) protocols. The MAC for Ethernet and for wireless systems is fundamentally based on avoiding and/or detecting and correcting collisions, and collision in this sense often appears in the name of such protocols, for example, CSMA/CA refers to Carrier Sense Multiple Access/Collision Avoidance.
A further aspect of the present invention provides a method of securing communications between a first transmitter and a receiver, the method including the steps of:
transmitting a message from the first transmitter over one or more of a range of communication channels;
transmitting noise from a second transmitter over said range of communications channels; passing to the receiver information about the noise from the second transmitter; retrieving, from the transmissions over said range of communications channels, the transmitted message using the information from the second transmitter.
The step of retrieving may include receiving a combination of the transmitted message and the transmitted noise in the receiver, and separating the transmitted message from that combination using said information.
Alternatively, or additionally, the step of retrieving may include selectively receiving on only a portion of said range of communications channels, so as to only receive the message, said portion being determined using said information.
In one embodiment of the method of this aspect, the second transmitter and the receiver are part of the same device.
Preferably, the content of the noise signals is substantially identical to the transmissions made by the, or each first transmitter. The advantages of this feature have been explained in relation to the first aspect above.
The range of communication channels may include one or more of: different time slots; different frequency bands; different orthogonal codes.
Preferably, the method further includes the step of detecting when a collision occurs between a part of the message transmitted by the first receiver and the noise transmitted by the second receiver, and retransmitting the part of the message affected.
The method of the present aspect may be implemented in a system of either of the first two aspects, including any combination of the optional or preferred features of those aspects.